<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        let num=new Number(99);
        console.log(num+1);
        console.log(typeof num);//Object

        let numb1=99;
        console.log(numb1.toString()+1);991

        // let Date1=new Date();
        // console.log(Date1.toString());
    //   let num11=new Number("99");
    //   let num22=Number("99");
    //   console.log(typeof num11);//Object
    //   console.log(typeof num22);//number

    //  console.log( Number.NaN);

    //是否为数字
    let number1=99;
    console.log(Number.isInteger(number1));
  
      let number2=99.520;
      console.log(number2.toFixed(2));//保留小数几位
 
    </script>
</body>
</html>